The invention relates to digital voice enhancement, DVE, communication systems, and more particularly to feedback instability detection and corrective action.
The invention may be used in duplex systems, for example as shown in U.S. Pat. No. 5,033,082, and U.S. application Ser. No. 08/927,874, filed Sep. 11, 1997, simplex systems, for example as shown in U.S. application Ser. No. 09/050,511, filed Mar. 30, 1998, all incorporated herein by reference, and in other systems.
The DVE communication system includes a first acoustic zone, a second acoustic zone, a microphone at the first zone, and a loudspeaker at the second zone and electrically coupled to the microphone such that the speech of a person at the first zone can be heard by a person at the second zone as transmitted by an electrical signal from the microphone to the loudspeaker.
Under adverse conditions, instabilities can inadvertently cause feedback in DVE systems. This feedback causes the DVE controller outputs to diverge unbounded at the frequency of instability. The end result is a loud objectionable tonal squeal or screech that grows in magnitude. This is an abnormal operational state of the DVE system which must be detected and suppressed.
The present invention uses signal statistics of the electrical signal transmitted to the loudspeaker to detect a condition of instability. An instability detector detects an unstable acoustic feedback condition from the loudspeaker to the microphone by sensing a condition of the electrical signal transmitted from the microphone to the loudspeaker, and a corrective processor responds to the instability detector to modify the noted electrical signal to reduce unstable acoustic feedback.